It is often necessary to provide two signals of a same frequency that have a specified phase difference therebetween over a broad bandwidth. For example, in a homodyne receiver, an input channel is transmitted to two mixers, and separate Local Oscillators generate output signals that have a same frequency and are 90 degrees out of phase with each other to drive the mixers. Various arrangements are known for generating two signals having a same frequency and a predetermined phase difference for specific purposes.
U.S. Pat. No. 4,330,854, issued to R. Zeitraeg on May 18, 1982, discloses apparatus for generating an exchange pulse train for use in a telecommunications system. The apparatus comprises first and second frequency adjustment phase locked loops which each receive a same standard pulse train at a predetermined frequency. The first and second phase locked loops generate a first and a second output master pulse train, respectively, and ensure that the two output master pulse trains are within a required predetermined frequency tolerance. The first and second master pulse trains are provided as inputs to a first and a second exchange pulse generator, respectively. Each of the first and second exchange pulse generators comprise a phase discriminator (PD), a low-pass filter, and a Voltage Controlled Oscillator (VCO) in series with a Frequency reducer in a feedback loop between the VCO and the PD, and produces a separate intermediate pulse train which is less than or equal to a predetermined maximum phase difference. One of a first and a second Frequency Reducer and Phase Synchronizer devices in the first and second exchange pulse generators, respectively, outputs a received exchange pulse train. Concurrently, the other Frequency Reducer and Phase Synchronizer compares the first and second intermediate pulse trains and produces an output exchange pulse train which is adjusted to have a same frequency as the other intermediate pulse train and to be within a predetermined phase tolerance.
U.S. Pat. No. 4,683,444, issued to O. Kappeler on Jul. 28, 1987, discloses a generator circuit for use in the field of analog quadrature mixture. The generator either generates first and second oscillator output signals or divides the output from a main oscillator into two oscillator output signals, and separately processes each oscillator output signal to generate two frequency variable sinusoidal output signals which are phase shifted by 90 degrees. In processing the two oscillator output signals, the second oscillator output signal is phase shifted by 90 degrees and each of the first oscillator signal and the second delayed oscillator output signal is separately multiplied with the other oscillator output signal before being separately low pass filtered in order to generate the two sinusoidal output signals.
U.S. Pat. No. 4,943,787, issued to M. Swapp on Jul. 24, 1990, discloses a digital time base generator for generating start and stop signals from a reference signal having a predetermined reference frequency. The reference signal is provided as an input to first and second phase locked loops (PLL) each comprising a VCO. Each PLL multiplies the reference frequency of the reference signal by a different predetermined integer amount than used by the other PLL. The resulting output signals are divided by separate dual modulus frequency dividers back down to the original reference frequency to produce the separate start and stop digital timing signals which have different waveform edges.
It is desirable to provide a relatively inexpensive and simple arrangement which generates a first and a second output signal having a selective predetermined constant phase difference therebetween from a single input reference signal, where the constant phase difference is maintainable when the input signal is varied over a wide frequency range.